A variety of techniques exist to model the color response of a halftone imaging device. Accurate modeling is important in achieving reliable, consistent color output from the imaging device. In particular, the model can be used to formulate device profiles. A device profile, such as an International Color Consortium (ICC) profile, permits generation of a color map defining device drive values based on image data so that the device produces an accurate representation of the color image defined by the image data. Notably, a model can reduce the need for extensive empirical color correction. In some cases, for example, a change in the physical characteristics of an imaging device can be accommodated by incremental adjustments to the model, rather than empirical measurements, which can be labor- and time-intensive.
One well known spectral modeling technique is the Neugebauer color mixing model. The Neugebauer model characterizes spectral reflectance in terms of a weighted sum of reflectances obtained from one-, two- and three-color combinations of available colorants and a substrate on which the colorants are formed. The resulting colorant combinations are referred to as the Neugebauer primaries. In a three-color system, e.g., having cyan, magenta, yellow (CMY) colorants, there are eight Neugebauer primaries. In a four-color system, e.g., having cyan, magenta, yellow, black (CMYK) colorants, there are sixteen Neugebauer primaries.
The Neugebauer model is widely used in the graphic arts industry to characterize the color response of halftone printing devices. However, certain modifications to the Neugebauer model have been developed over the years to enhance accuracy. For example, existing implementations of the Neugebauer model typically incorporate a dot gain value that characterizes differences between theoretical halftone dot size and the actual dot size that is produced upon transfer of a colorant from a printing plate to paper.
In addition, many Neugebauer implementations take into account the penetration of light into paper, and characterize this effect in terms of the Yule-Nielson “n factor.” Initially, the penetration represented by the n factor was expressed as a function of wide band reflectance. More recently, the n factor has been expressed in terms of narrow-band spectral curves.